The Skeletal System

About this topic

The skeleton gives support, protects organs (skull protects the brain, ribs the lungs), enables movement with muscles, makes blood cells in bone marrow and stores minerals like calcium. An adult has 206 bones, while babies have more, many of which fuse.

Joints connect bones: ball-and-socket joints (hip) allow wide movement, hinge joints (knee) move one way, and fixed joints (skull) don't move. Ligaments join bone to bone, and cartilage cushions joints. Bone is living tissue that repairs itself.

An infant has about 300 bones, many of which fuse as they grow into the 206 of an adult. Joints include ball-and-socket joints like the hip, allowing wide movement, and hinge joints like the knee, allowing movement in one plane. Cartilage cushions the ends of bones, and ligaments join bone to bone.

Bones are living tissue that can repair themselves after fractures and strengthen with weight-bearing exercise. Osteoporosis, common in older women, makes bones brittle and is made less likely by calcium, vitamin D and exercise. Red marrow in flat bones makes blood cells. A frequent misconception is that bones are dry and dead; they have blood vessels, nerves and cells. Also, tendons join muscle to bone, not ligaments.